code: def forward(self, x, edge_index):
      edge_index, _ = add_self_loops(edge_index, num_nodes=x.size(0))
  
      row, col = edge_index
      deg = degree(row, x.size(0), dtype=x.dtype)
      deg_inv_sqrt = deg.pow(-0.5)
      norm = deg_inv_sqrt[row] * deg_inv_sqrt[col]
  
      x = self.lin(x)
      return self.propagate(
          edge_index, size=(x.size(0), x.size(0)), x=x, norm=norm
      )
  
file_path: pytorch_geometric/test/nn/conv/test_create_gnn.py
imports: import torch
  from torch_geometric.nn import MessagePassing
  from torch_geometric.utils import add_self_loops, degree
label_desc: Use image node_id 2 for calling the GCNConv obj's underlying member method code with example usage: obj.forward(x, edge_index) and returns: self